A Sensitive Triple Quadrupole Liquid Chromatography Mass Spectrometric Method for the Estimation of Valproic Acid in K2EDTA Human Plasma using Furosemide as the Internal Standard.

A valproic acid is primarily being used in the treatment of epilepsy is a histone deacetylase inhibitor and it is under investigation for treatment of HIV and various cancer indications. A specific, sensitive and fast bioanalytical LC-MS/MS method was developed with furosemide as an internal standard (IS) and thoroughly validated for the quantitation of valproic acid using turbo ion spray in negative ion mode. The analyte and IS was extracted using protein precipitation. The chromatographic separation of analytes from extracted matrix was achieved using a Chromolith RP 18e (2.0×50 mm) column with a gradient mobile phase comprising of acetonitrile and purified water with acetic acid. The elution of both peaks was achieved within 5.2 min, with retention times of 2.55 min and 1.67 min for valproic acid and IS, respectively. Quantitation of valproic acid was achieved by the pseudo SRM transition pairs (m/z 142.8→m/z 142.8), and SRM transition pair (m/z 328.8 →m/z 204.6) for internal standard.The calibration standards of valproic acid showed linear over a range from 50 to 40 000 ng/mL, with a lower limit of quantitation of 50 ng/mL with accuracy of 3.74% and precision of 5.06%. The bias for inter- and intra-batch assays was 1.24-6.14% and 3.85-11.84%, respectively; while the corresponding precision was 2.56-16.37% and 1.29-11.34%, respectively. The developed method was used to monitor valproic acid levels in clinical samples. Because of higher sensitivity, this method can be used for therapeutic drug monitoring in pediatric subjects.

Predictions of the Pharmacokinetics in Burn Injury Patients using Regression Models - Case Study with Levofloxacin.

Owing to its excellent safety, tolerability, pharmacokinetic and pharmacodynamic profile levofloxacin is widely used. Although pharmacokinetics of levofloxacin was somewhat more variable in burn injury patients, it appeared to be comparable to healthy subjects or other patients. Linear regression model was established for Cmax or Cmin vs. [AUCtau, CL and Vd] of levofloxacin using individual values from burn injury patients. Appropriate regression lines for Cmax or Cmin were subjected to internal and external validation on the ability to predict CL, Vd and AUCtau parameters. The mean absolute error (MAE) and root mean square error (RMSE) of the predictions were used to judge the appropriateness of either Cmax or Cmin models. Cmax models developed for levofloxacin showed moderate to strong correlations with the various parameters such as CL, Vd and AUCtau. The Cmin models showed strong correlation for CL and AUCtau but not for Vd where the correlation was weak. Internal validation using data from individual burn patients showed RMSE of 13.47-25.42% for various predictions. External validation that used mean data from healthy subjects showed RMSE of 13.86-27.13%. Despite the pharmacokinetic variability, linear regression models using either Cmax or Cmin were established for levofloxacin rendering predictions of several key pharmacokinetic parameters. Although there was limitation of Cmin model for predicting Vd, both models may be used as a prospective tool for the prediction of levofloxacin pharmacokinetics in burn care patients.

Dual Incorporation of the in vitro Data (IC50) and in vivo (Cmax) Data for the Prediction of Area Under the Curve (AUC) for Statins using Regression Models Developed for Either Pravastatin or Simvastatin.

Linear regression models utilizing a single time point (Cmax) has been reported for pravastatin and simvastatin. A new model was developed for the prediction of AUC of statins that utilized the slopes of the above 2 models, with pharmacokinetic (Cmax) and a pharmacodynamic (IC50 value) components for the statins. The prediction of AUCs for various statins (pravastatin, atorvastatin, simvastatin and rosuvastatin) was carried out using the newly developed dual pharmacokinetic and pharmacodynamic model. Generally, the AUC predictions were contained within 0.5 to 2-fold difference of the observed AUC suggesting utility of the new models. The root mean square error predictions were<45% for the 2 models. On the basis of the present work, it is feasible to utilize both pharmacokinetic (Cmax) and pharmacodynamic (IC50) data for effectively predicting the AUC for statins. Such a new concept as described in the work may have utility in both drug discovery and development stages.

Infusion Rate Dependent Pharmacokinetics of Bendamustine with Altered Formation of γ-hydroxybendamustine (M3) Metabolite Following 30- and 60-min Infusion of Bendamustine in Rats.

Bendamustine is an alkylating agent administered as 1 h intravenous infusion in the clinic for the treatment of malignant haematological cancers. The aim of the study was to evaluate the pharmacokinetics of bendamustine and its key cytochrome P 450 (CYP) 1A2 mediated γ-hydroxybendamustine (M3) metabolite after 30- and 60-min intravenous infusion of bendamustine in rats. 2 groups were assigned to receive bendamustine either as 30- or 60-min infusion and doses were normalized to 15 mg/kg for the sake of statistical evaluation. Serial pharmacokinetic samples were collected and were analysed for the circulatory levels of bendamustine and its M3 metabolite. Standard pharmacokinetic parameters were generated for bendamustine and its M3 metabolite. Regardless of the intravenous regimens, Cmax coincided with end of infusion for both bendamustine and its M3 metabolite. Immediately after stoppage of infusion, a rapid decline in the plasma levels occurred for both bendamustine and M3 metabolite. The Cmax and AUC0-∞ parameters for bendamustine after 60-min infusion were 1.90 and 1.34-fold higher; while CL was lower by 1.32-fold as compared to the 30-min infusion. In contrast, the Cmax and AUC0-∞ after 30-min infusion for the M3 metabolite was 2.15- and 2.78-fold greater; while CL was 2.32-fold lower when compared to the 60-min infusion. However, T1/2 and Vz values were similar between the 2 intravenous treatments for bendamustine or the M3 metabolite. The data unequivocally confirmed the existence of differential pharmacokinetics of bendamustine and its M3 metabolite as the function of the duration of intravenous infusion.

Limited Sampling Strategy for the Prediction of Area Under the Curve (AUC) of Statins: Reliability of a Single Time Point for AUC Prediction for Pravastatin and Simvastatin.

Statins are widely prescribed medicines and are also available in fixed dose combinations with other drugs to treat several chronic ailments. Given the safety issues associated with statins it may be important to assess feasibility of a single time concentration strategy for prediction of exposure (area under the curve; AUC). The peak concentration (Cmax) was used to establish relationship with AUC separately for pravastatin and simvastatin using published pharmacokinetic data. The regression equations generated for statins were used to predict the AUC values from various literature references. The fold difference of the observed divided by predicted values along with correlation coefficient (r) were used to judge the feasibility of the single time point approach. Both pravastatin and simvastatin showed excellent correlation of Cmax vs. AUC values with r value ≥ 0.9638 (p<0.001). The fold difference was within 0.5-fold to 2-fold for 220 out of 227 AUC predictions and >81% of the predicted values were in a narrower range of >0.75-fold but <1.5-fold difference. Predicted vs. observed AUC values showed excellent correlation for pravastatin (r=0.9708, n=115; p<0.001) and simvastatin (r=0.9810; n=117; p<0.001) suggesting the utility of Cmax for AUC predictions. On the basis of the present work, it is feasible to develop a single concentration time point strategy that coincides with Cmax occurrence for both pravastatin and simvastatin from a therapeutic drug monitoring perspective.

Tumebacillus lipolyticus sp. nov., isolated from river water.

An aerobic, endospore-forming, alkali-tolerant, Gram-stain-positive, non-motile, rod-shaped bacterium, designated strain NIO-S10T, was isolated from a surface water sample collected from the Godavari River, Kapileswarapuram, India. Colonies on nutrient agar were circular, 3-4 mm in diameter, creamish and raised after incubation for 36 h at 37 °C. Growth occurred at 20-40 °C, at pH 6-9 and in the presence of 0-2 % (w/v) NaCl. Strain NIO-S10T was positive for oxidase, caseinase, DNase, gelatinase, lipase and urease activities, and negative for catalase, aesculinase, amylase and cellulase activities. The fatty acids were dominated by branched and saturated fatty acids, with a high abundance of iso-C15 : 0, anteiso-C15 : 0 and C18 : 0.The cell-wall peptidoglycan contained meso-diaminopimelic acid as the diagnostic diamino acid, and MK-7 was the major menaquinone. The DNA G+C content of strain NIO-S10T was 54.4 mol%. A blast sequence similarity search based on 16S rRNA gene sequences indicated that Tumebacillus ginsengisoli Gsoil 1105T was the nearest phylogenetic neighbour to strain NIO-S10T, with a pairwise sequence similarity of 94.9 %. Phylogenetic analysis showed that strain NIO-S10T was clustered with members of the genus Tumebacillus and together with members of the genus Effusibacillus. Based on phenotypic characteristics and phylogenetic inference, strain NIO-S10T represents a novel species of the genus Tumebacillus, for which the name Tumebacillus lipolyticus sp. nov. is proposed. The type strain is NIO-S10T ( = KCTC 32289T = MTCC 12483T).